How Colorblindness Works

How do you see through someone else's eyes? It's difficult to say how someone else sees color, because it's so subjective. How do I know that what I see as red is what you see as red? Is my red richer and bolder than yours? Or faded and dim compared to what you see? You may have argued with someone over whether a pair of pants is navy blue or black and never quite seen eye to eye.

When you refer to a rainbow of colors, you think ROYGBIV: red, orange, yellow, green, blue, indigo, violet. So what does someone who's colorblind see? Nothing that varied and exciting.

With this brightly colored image, we'll look at how deuteranopia and protanopia (both types of red-green colorblindness) as well as tritanopia affect how someone sees.

Deuteranopia: The reds are all gone. The woman's dress appears greenish-gray, and the purple has left her umbrella. The green from the umbrella looks rather grayish. Even her skin has lost its pinkish tone.

Protanopia: Looks a lot like deuteranopia, doesn't it? Except that the red dress has gone to a darker gray.

Tritanopia: The yellow in the image has turned to a light pink. There's no orange. The blue of the sky has changed and so have all the reds. What you're mostly seeing looks like shades of pink and blue. It's duller.

Anomalous trichromats have trouble telling green, yellow and red apart. They may see no difference at all between the purple object you're holding up and the blue one (since the purple involves red light.)

A monochromat sees black, white and gray, and what he sees is probably rather blurry.

On the pros side, people who have mild red-green color deficiency are said to be better at detecting camouflage. Same with dichromats -- they're more attuned to texture, instead of being fooled by the patterns of color [source: Gene Reviews].

What do animals see?

Contrary to popular belief, dogs and cats don't see in shades of gray. They do see colors, just not all of the colors. Apes and some monkeys see like us. Raccoons are colorblind, and so are whales and seals, but manatees can tell blue from green. Birds see even better than we do.

Lots of animals also have ultraviolet vision -- from birds to bugs, fish to lizards. Interestingly, after an injury or an event like cataract surgery, some humans gain ultraviolet vision. When the lens of a person's eye has been removed, the condition is called aphakia. Some people think Monet had the condition after his cataract surgery -- he claimed that the colors he saw had completely changed and were in fact "quite terrifying" [source: Fortune]. (Bonus fact: The urine of many rodent species reflects ultraviolet light, which may be why rodents have retained UV vision, unlike other mammals [source: National Geographic].)